The present invention relates to seals between a movable airfoil member and the structure to which it is mounted, and more particularly, to a seal assembly for sealing the mounting hole in a vertical stabilizer through which the structural mounting member of a flying horizontal stabilizer extends.
Many aircraft employ variable incidence, horizontal airfoil surfaces, and especially horizontal stabilizer surfaces, to trim aircraft attitude during flight and to complement conventional control surfaces such as the elevator associated with a horizontal stabilizer. In such assemblies, the horizontal airfoil is coupled to the body of the aircraft for relative swinging movement, and in the case of an aircraft employing a T-tail configuration, a horizontal stabilizer surface is mounted on the vertical stabilizer for pivotal movement about a hinge axis transverse to the chord of the verical stabilizer.
In the latter instance, prior art construction techniques have required the addition of a shaped fairing member affixed to the central portion of the horizontal stabilizer that extends over and surrounds the upper end of the vertical stabilizer. These fairing assemblies are sometimes referred to as top hats. An additional fairing is affixed to the horizontal stabilizer and moves with the horizontal stabilizer as its incidence is varied when it is swung about its hinge axis. Such fairings are necessitated for several reasons, including the provision of aerodynamic structure to cover or surround the hinge structure for the horizontal stabilizer and the actuating means for varying its incidence. In addition the horizontal stabilizer and top hat are conventionally provided with a seal member between the moving portion of the horizontal stabilizer and top hat and the outer surface of the vertical stabilizer to prevent disturbance of the aerodynamic flow of air across the stabilizers that would oridinarily be caused by the gap between the horizontal stabilizer, the top hat and the vertical stabilizer surfaces. Because of the airfoil shape of the vertical stabilizer and the predetermined shape of the top hat and horizontal stabilizer, a seal surface is usually formed by reshaping the verical stabilizer in the region across which the edges of the top hat and horizontal stabilizer swing as the incidence of the latter is varied. The reshaping is necessary to provide a constant gap between the horizontal stabilizer and the vertical stabilizer so that a seal member can be effectively interposed to maintain a seal between the horizontal stabilizer and the vertical stabilizer at any position of the former. Such reshaping to the vertical stabilizer surface adjacent the area wiped by the seal necessitates additional structure, in turn greatly increasing the required weight and expense for constructing an empennage assembly employing a flying horizontal stabilizer, destroys the airfoil efficiency or a portion of the vertical stabilizer, and at the same time increases the drag on the aircraft.
It is a broad object of the invention to provide a seal assembly for sealing at least a portion of a variable incidence airfoil to aircraft structure on which it is mounted. It is a further object of the present invention to provide a T-tail construction for an aircraft that eliminates the need for a large, central aerodynamic fairing or top hat on the horizontal stabilizer and that eliminates the necessity for reshaping the airfoil of the vertical stabilizer under the area wiped by a seal associated with a flying horizontal stabilizer. Additional objects of the invention are to provide a T-tail assembly having a flying horizontal stabilizer that is easily manufactured and assembled and on which the seal structure can be adjusted after the major components of the T-tail are assembled, and to provide a seal member that can easily be replaced and maintained.